Etching substrates using ale and selective deposition

ABSTRACT

Methods of and apparatuses for processing substrates having carbon-containing material using atomic layer deposition and selective deposition are provided. Methods involve exposing a carbon-containing material on a substrate to an oxidant and igniting a first plasma at a first bias power to modify a surface of the substrate and exposing the modified surface to an inert plasma at a second bias power to remove the modified surface. Methods also involve selectively depositing a second carbon-containing material onto the substrate. ALE and selective deposition may be performed without breaking vacuum.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims benefit of U.S. Provisional Patent ApplicationNo. 62/329,916, filed Apr. 29, 2016, and titled “ETCHING SUBSTRATESUSING ALE AND SELECTIVE DEPOSITION,” which is incorporated by referenceherein in its entirety and for all purposes.

BACKGROUND

Patterning methods are critical to semiconductor processing. Inparticular, extreme ultraviolet (EUV) lithography has been explored toextend lithographic technology beyond its optical limits and replacecurrent photolithography methods to pattern small critical dimensionfeatures. Current EUV lithography methods result in poor edge roughnessand weak patterns that may ultimately render the substrate useless.

SUMMARY

Provided herein are methods and apparatuses for processing semiconductorsubstrates. One aspect involves a method of processing substrates, themethod including: (a) exposing a substrate including a firstcarbon-containing material to an oxidant and igniting a first plasmawith a first bias power to modify a surface of the firstcarbon-containing material; and (b) exposing the modified layer to asecond plasma at a second bias power and for a duration sufficient toremove the modified surface without sputtering. In various embodiments,the method also includes (c) selectively depositing a secondcarbon-containing material on the substrate to fill crevices on thefirst carbon-containing material. In various embodiments, the methodalso includes repeating (a)-(c) in cycles. In various embodiments, thesecond bias power may be between about 30V and about 100V.

In some embodiments, the oxidant is a strong oxidant. For example, thestrong oxidant may be oxygen. In various embodiments, the first plasmais generated using a plasma power between about 15 W and about 500 W.The first bias power may be between about 5V and 50V.

In some embodiments, the oxidant is a weak oxidant. For example, theweak oxidant may be any one or more of carbon dioxide, carbon monoxide,sulfur dioxide, nitric oxide, nitrogen, and ammonia. In someembodiments, the first plasma is generated using a plasma power betweenabout 30 W and about 500 W. The first bias power may be between about30V and about 100V.

In various embodiments, selectively depositing the secondcarbon-containing material on the substrate includes applying aself-bias at a power between about 5V and about 15V and igniting aplasma using a plasma power between about 30 W and about 500 W. In someembodiments, selectively depositing the second carbon-containingmaterial on the substrate also includes introducing methane. Selectivelydepositing the second carbon-containing material on the substrate mayalso include introducing a diluent such as any one or more of nitrogen,helium, argon, hydrogen, and combinations thereof.

In various embodiments, the first carbon-containing material is any oneor more of photoresist, amorphous carbon, and graphene. In someembodiments, the first carbon-containing material is a photoresistpatterned by extreme ultraviolet lithography.

In some embodiments, (c) includes exposing the substrate to methane toadsorb a layer of methane to the surface of the first carbon-containingmaterial and exposing the substrate to a third plasma.

The third plasma may be generated by introducing an inert gas such asany one or more of helium, hydrogen, nitrogen, argon, and neon andigniting a plasma.

In various embodiments, exposing the substrate including the firstcarbon-containing material to the oxidant also includes exposing thesubstrate to a diluent inert gas such as any one or more of helium,argon, neon, krypton, and xenon.

The second plasma in (b) may be generated by introducing an inert gassuch as any one or more of hydrogen, helium, nitrogen, argon, and neonand igniting a plasma.

In various embodiments, the method also includes purging a chamberhousing the substrate between performing (a) and (b) to remove excessoxidant from the chamber.

In some embodiments, the method also includes repeating (a) and (b) incycles.

The substrate may rest on a pedestal set to a temperature between about0° C. and about 120° C.

Another aspect involves an apparatus for processing a substrate, theapparatus including: one or more process chambers, each process chamberincluding a chuck; one or more gas inlets into the process chambers andassociated flow control hardware; and a controller having at least oneprocessor and a memory, such that the at least one processor and thememory are communicatively connected with one another, the at least oneprocessor is at least operatively connected with the flow controlhardware, and the memory stores computer executable instructions forcontrolling the at least one processor to at least control the flowcontrol hardware by: (i) introducing an oxidant to the process chamberand igniting a first plasma at a first bias power; and (ii) introducinga first inert gas and igniting a second plasma at a second bias powersuch that (i) and (ii) are performed without breaking vacuum.

In various embodiments, the memory also includes instructions for (iii)introducing a carbon-containing precursor to the process chamber to forman adsorbed layer of the carbon-containing precursor to the surface of asubstrate housed in the one or more process chambers; and (iv)introducing a second inert gas and igniting a third plasma.

In various embodiments, the instructions further include instructionsfor turning on a self-bias at a power between about 5V and about 15Vwhen introducing the carbon-containing precursor in (iii).

In various embodiments, the instructions further include instructionsfor introducing a diluent selected from the group consisting ofnitrogen, helium, argon, hydrogen, and combinations thereof.

In various embodiments, the oxidant is oxygen. The first bias power maybe between about 5V and about 50V. In various embodiments, the firstplasma is set to a plasma power between about 15 W and 500 W.

In various embodiments, the oxidant is any one or more of carbondioxide, carbon monoxide, sulfur dioxide, nitric oxide, nitrogen, andammonia. In some embodiments, the first bias power is between about 30Vand about 100V. In some embodiments, the first plasma is set to a plasmapower between about 30 W and 500 W.

These and other aspects are described further below with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an example of atomic layer etchingof film on a substrate.

FIG. 2 is a schematic illustration of an example of performing atomiclayer etching on a resist with a protrusion.

FIG. 3 is a schematic illustration of an example of a removal operationduring atomic layer etching.

FIG. 4 is a schematic illustration of a selective deposition cycle thatmay be used in accordance with certain disclosed embodiments.

FIG. 5 is a process flow diagram of operations performed in accordancewith disclosed embodiments.

FIG. 6 is a schematic diagram of an example process chamber forperforming certain disclosed embodiments.

FIG. 7 is a schematic diagram of an example process apparatus forperforming certain disclosed embodiments.

FIG. 8A is an image of a substrate used in an experiment.

FIG. 8B is an image of a substrate from an experiment.

FIGS. 8C-8E are images of resulting substrates from experimentsconducted in accordance with certain disclosed embodiments.

FIGS. 9A-9C are various views of substrates.

FIGS. 10A-10C and 11A-11C are various view of a substrate from anexperiment conducted in accordance with certain disclosed embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a thorough understanding of the presented embodiments. Thedisclosed embodiments may be practiced without some or all of thesespecific details. In other instances, well-known process operations havenot been described in detail to not unnecessarily obscure the disclosedembodiments. While the disclosed embodiments will be described inconjunction with the specific embodiments, it will be understood that itis not intended to limit the disclosed embodiments.

Patterning of thin films in semiconductor processing is used in themanufacture and fabrication of semiconductor devices. Conventionalpatterning involves photolithography, such as 193 nm lithography. Inphotolithography, patterns are printed by emitting photons from a photonsource onto a mask and printing the pattern onto a photosensitivephotoresist, thereby causing a chemical reaction in the photoresist thatremoves certain portions of the photoresist to form the pattern. Asdevices shrink, the need for printing smaller features increases.Although multiple patterning techniques have been developed for use withconventional photolithography, multiple patterning uses multiple layersof deposition and etching processes. Scaling of features on advancedsemiconductor integrated circuits (ICs) and other devices has drivenlithography to improve resolution by moving to ever smaller imagingsource wavelengths.

Extreme ultraviolet (EUV) lithography has been developed to printsmaller patterns on a photoresist using EUV light sources atapproximately 13.5 nm wavelength in leading-edge lithography tools,which are also referred to as scanners. Although next generation EUV wasfirst expected in 2006 to support 45 nm technology node manufacturing,such developments have been long delayed due to several productivityissues. One challenge in EUV productivity has been generating sufficientpower to perform patterning due to the inherent difficulty creating andfocusing 13.5 nm photons. The system throughput, and hence overall costand productivity, is determined by the ratio of photons delivered at thewafer to the photons required to image the photoresist. Although therehave been methods developed over the last decade directed to modifyingthe source, methods have not yet achieved a source power of 250 W for a45 nm technology node to permit efficient use of EUV techniques. Thesource power used to perform EUV increases as devices shrink due to shotnoise and resist blur such that to perform EUV in the 5 nm technologynode, a source power of 500 W-1000 W is used to be cost competitive withexisting patterning technologies.

Insufficient source power results in a loss of pattern fidelity, both inthe edge roughness of patterned images as well as in the definedcritical dimension, particularly for via imaging. This is due to, inaddition to other reasons, the low number of photons available to imageeach via, stochastic variations in the number of photons in each featureand the efficiency of each photon in creating a photoacid result inrandom variations in hole size (also referred to as local criticaldimension uniformity, or “LCDU” as referred to herein) and edgeroughness (also referred to as line edge roughness, or “LER” as referredto herein).

Current techniques for patterning photoresists for small criticaldimension devices includes a reactive ion etching (“RIE”) process toharden, smooth, and remove residue from a photoresist. However, currentRIE processes are unable to address LER or LCDU. For example,photoresists that have been processed by RIE may still include smallstringers between features and resist scum on the bottom of features.

Provided herein are methods of etching substrates such as photoresiststo generate uniformly etched and smooth edges in imaged features afterphotolithography. Such techniques improve both LER and LCDU as describedherein. Disclosed embodiments reduce the need for using a high sourcepower to perform EUV applications, thereby improving EUV scannerproductivity. Disclosed embodiments are suitable for etching substratesto form structures such as contacts to a source/drain region, 3-Dcontact holes, and more.

Methods involve atomic layer etching (ALE) and selective deposition togently etch and smooth material such as carbon-containing material.Example carbon-containing material that may be etched using disclosedembodiments include photoresists (such as those used in EUV orimmersion) and amorphous carbon.

ALE is a technique that removes thin layers of material using sequentialself-limiting reactions. Generally, ALE may be performed using anysuitable technique. Examples of atomic layer etch techniques aredescribed in U.S. Pat. No. 8,883,028, issued on Nov. 11, 2014; U.S. Pat.No. 8,808,561, issued on Aug. 19, 2014; and U.S. Pat. No. 9,576,811,issued on Feb. 21, 2017, which are herein incorporated by reference forpurposes of describing example atomic layer etch and etching techniques.In various embodiments, ALE may be performed with plasma, or may beperformed thermally.

ALE may be performed in cycles. The concept of an “ALE cycle” isrelevant to the discussion of various embodiments herein. Generally anALE cycle is the minimum set of operations used to perform an etchprocess one time, such as etching a monolayer. The result of one cycleis that at least some of a film layer on a substrate surface is etched.Typically, an ALE cycle includes a modification operation to form areactive layer, followed by a removal operation to remove or etch onlythis modified layer. The cycle may include certain ancillary operationssuch as sweeping one of the reactants or byproducts. Generally, a cyclecontains one instance of a unique sequence of operations. As an example,an ALE cycle may include the following operations: (i) delivery of areactant gas (adsorption), (ii) purging of the reactant gas from thechamber, (iii) delivery of a removal gas and an optional plasma(desorption), and (iv) purging of the chamber.

FIG. 1 shows two example schematic illustrations of an ALE cycle and aschematic illustration of selective polymer deposition. Diagrams 171a-171 e show an example ALE cycle. In 171 a, the substrate is provided.

In various embodiments, the substrate may be a silicon wafer, e.g., a200-mm wafer, a 300-mm wafer, or a 450-mm wafer, including wafers havingone or more layers of material, such as dielectric, conducting, orsemi-conducting material deposited thereon. In some embodiments, thesubstrate includes a blanket layer of silicon, such as amorphoussilicon, or a blanket layer of germanium. The substrate may include apatterned mask layer previously deposited and patterned on thesubstrate. For example, a mask layer may be deposited and patterned on asubstrate including a blanket amorphous silicon layer. In someembodiments, the substrate surface includes a photoresist, or graphene,or amorphous carbon.

In some embodiments, the layers on the substrate may be patterned.Substrates may have “features” such as via or contact holes, which maybe characterized by one or more of narrow and/or re-entrant openings,constrictions within the feature, and high aspect ratios. The featuremay be formed in one or more of the above described layers. One exampleof a feature is a hole or via in a semiconductor substrate or a layer onthe substrate. Another example is a trench defined by a line or space ina substrate or layer. In various embodiments, the feature may have anunder-layer, such as a barrier layer or adhesion layer. Non-limitingexamples of under-layers include dielectric layers and conductinglayers, e.g., silicon oxides, silicon nitrides, silicon carbides, metaloxides, metal nitrides, metal carbides, and metal layers. In someembodiments, the surface of the substrate may include more than one typeof material, such as if the substrate is patterned. The substrateincludes at least one material to be etched and smoothened usingdisclosed embodiments. This material may be any of those describedabove—metals, dielectrics, semiconductor materials, and others. Invarious embodiments, these materials may be prepared for fabricatingcontacts, vias, gates, etc. In some embodiments, the material to beetched is a hard mask material, such as amorphous carbon. Furtherexample materials include aluminum gallium nitride, silicon, galliumnitride, tungsten, and cobalt.

In 171 b, the surface of the substrate is modified. In 171 c, themodified layer remains after a purge operation to remove excessnon-adsorbed precursor. In 171 d, the modified layer is being etched. In171 e, the modified layer is removed.

Similarly, diagrams 172 a-172 e show an example of an ALE cycle foretching a carbon-containing film. In 172 a, a substrate includingcarbon-containing material is provided, which includes many carbonatoms. In various embodiments, the substrate includes acarbon-containing layer such as a photoresist or amorphous carbon layer.

In 172 b, an oxidant is introduced to the substrate which modifies thesurface of the substrate. The oxidant may be a strong oxidant such asoxygen (O₂) or a weak oxidant such as carbon dioxide (CO₂). Theselection of oxidants may depend on the type of carbon-containingmaterial on the substrate. For example, in some embodiments, a strongoxidant may be an oxidant suitable to etch hard carbon-containingmaterial, such as amorphous carbon or graphene. In another example, insome embodiments, a weak oxidant may be an oxidant suitable for etchingphotoresists patterned by EUV (extreme ultraviolet) lithography orimmersion lithography.

The schematic in 172 b shows that some oxidant is adsorbed onto thesurface of the substrate as an example. The modification operation formsa thin, reactive surface layer with a thickness that is more easilyremoved than the un-modified material in the subsequent removaloperation. For etching a carbon-containing material, anoxygen-containing plasma may be used during the modification oradsorption operation. Oxygen-containing plasma may be generated byflowing an oxygen-containing modification chemistry such as oxygen (O₂)or a weak oxidant such as carbon dioxide (CO₂) and igniting a plasma.Additional weak oxidants include carbon monoxide (CO), nitrogen oxide(NO), and sulfur dioxide (SO₂). Additional reactants may includenitrogen, hydrogen, and ammonia compounds and species which can bereactively bound to the resist surface and subsequently volatized usinga sub-sputter threshold ion bombardment. These strong and weak oxidantsmay be used by themselves or in combination, including with diluentinert gases such as helium (He), argon (Ar), neon (Ne), krypton (Kr),xenon (Xe), and combinations thereof. This operation modifies a fewangstroms of the carbon-containing material surface to form a modifiedlayer having weaker bond energies than bulk carbon-containing material.In various embodiments, the weak oxidant is provided to the substrate asa plasma with no or a low bias. For example, in various embodiments, theweak oxidant is introduced to a plasma processing chamber and a plasmasource power is turned on to ignite a plasma to facilitate adsorption ofthe weak oxidant onto the surface of the carbon-containing material. Thebias may be applied at a low power or voltage, such as a self-biasbetween about 5V and about 15V or up to about 50V. The plasma power maybe set at a power between about 15 W and about 300 W. It will beunderstood that the terms “bias power” and “bias voltage” are usedinterchangeably herein to describe the voltage for which a pedestal isset when a bias is applied to the pedestal. Bias power or bias voltageas described herein is measured in volts, which are indicated by theunit “V” or “Vb”, where b refers to bias.

In 172 c, the weak oxidant is purged from the chamber. In 172 d, aremoval gas argon is introduced with a directional plasma as indicatedby the Ar+ plasma species and arrows, and ion bombardment is performedto remove the modified carbon surface of the substrate. During thisoperation, a bias is applied to the substrate to attract ions toward it.In the desorption operation, an inert gas plasma (such as He, Ar, Xe, orN₂) may be used to remove the modified layer. Although argon is depictedin 172 d, it will be understood that any suitable inert gas may be usedto generate a plasma for this operation. The bias power applied duringremoval may be between about 30V and about 100V in various embodiments.The bias power may be selected such that the energy provided to thesubstrate is less than the energy required to sputter the substrate butgreater than the energy used to remove the modified layer from thesubstrate. The plasma power may be set at a power between about 30 W andabout 500 W.

In 172 e, the chamber is purged and the byproducts are removed. Invarious embodiments, between about 1 Å and about 130 Å of material maybe removed in one cycle. If a stronger oxidant is used, the etch ratemay be greater than if a weaker oxidant is used. For example, for astrong oxidant such as oxygen (O₂) the inert plasma gas may be Ar, andabout 10 Å to about 30 Å of resist material may be removed. In someembodiments, if the weak oxidant used is carbon dioxide and the inertgas plasma used to remove the modified layer is helium, each cycle mayetch between about 2 Å and 3 Å of material. The post etch surface of thecarbon-containing material is typically smooth after an ALE process. Forexample, in some embodiments, the root mean square roughness of thesurface after an ALE process may be less than about 0.5 nm (Rrms<0.5nm).

FIG. 2 shows how this operation can reduce the presence of protrusionson a photoresist. The size of protrusions on a photoresist may bebetween about 1 Å and about 30 Å in diameter and/or in height. Anexample substrate 200 having resist material and a protrusion 299 isprovided. The weak oxidant 201 is provided and adsorbs onto thesubstrate 200, which modifies the surface of the substrate 200 to formmodified surface 202. The modified surface 202 is then removed; thedotted line 203 shows where the previous carbon-containing material wason the substrate 200 to now yield substrate 210. This process 250 mayconstitute one ALE oxidation cycle. Process 260 shows a substrate 220having a protrusion 298, which is exposed to a weak oxidant 221. Theweak oxidant 221 adsorbs onto the substrate 220 which modifies thesurface of the substrate 220 to form modified surface 222. Weak oxidant231 adsorbs onto substrate 230 to form a modified layer (not shown) andthe modified layer is further removed to yield substrate 270, whichincludes a dotted line 275 showing where the previous carbon-containingmaterial was on the substrate 230.

Without being bound by a particular theory, it is believed that thescale of protrusions is on the atomic level such that since protrusionshave a greater surface to volume ratio, when the carbon-containingmaterial is adsorbed onto the surface of the protrusion and a monolayeror two of the protrusion is removed, the size of the protrusion issubstantially reduced relative to material removal from an adjacentrelatively flat portion of the surface. This may be due to morecarbon-containing material being adsorbed onto the greater surface areaprovided by the protrusion.

FIG. 3 shows how the removal operation can improve smoothing of thematerial being etched. The inert plasma species is used in 172 d with alow bias such that the plasma species has enough energy to remove themodified surface of weak oxidant adsorbed to carbon atoms on the surfaceof the substrate but does not have enough energy to sputter theunderlying non-modified carbon atoms from the surface of the substrate.In various embodiments, the bias may be between about 30V and about100V, or less than about 50V. In some embodiments, the modified layermay be about 0.5 nm thick, which may include about 3 to 4 atomic layers.In some embodiments there may be a phase boundary between the modifiedlayer and the amorphous material as shown in FIG. 3. The inert plasmaspecies, such as Ar+ shown in FIG. 3, may be a sub-threshold,non-reactive ion species, where sub-threshold means the energy of theinert plasma species is insufficient to sputter the material underlyingthe modified layer but high enough to remove the modified layer. Athreshold bias power or threshold bias voltage refers to the maximumvoltage of the bias applied to a pedestal before material on the surfaceof a substrate on the pedestal is sputtered. The threshold bias powertherefore depends in part on the material to be etched, the gas used togenerate plasma, plasma power for igniting the plasma, and plasmafrequency. After each cycle, the surface may be “reset” such thatsurface includes material to be removed without much or any modifiedmaterial on the surface.

Further description about smoothening substrates using ALE techniques isdescribed in U.S. Provisional Patent Application No. 62/214,813,entitled “ALE SMOOTHNESS: IN AND OUTSIDE SEMICONDUCTOR INDUSTRY” filedon Sep. 4, 2015, and U.S. Patent Application Publication No.2017/0069462, filed Aug. 31, 2016 and entitled “ALE SMOOTHNESS: IN ANDOUTSIDE SEMICONDUCTOR INDUSTRY”, which are herein incorporated byreference in their entireties. Without being bound by a particulartheory, it is believed that substrates may be smoothened by disclosedembodiments due to the layer-by-layer mechanism by which ALE etchesmaterial, thereby etching and smoothening protrusions on a surface ofthe substrate during each cycle. For example, a protrusion on thesurface of material to be smoothened may be modified and etched on thesurfaces of the protrusions such that as the protrusion is etched, thesize of the protrusion shrinks with each etching cycle, therebysmoothening the surface of the material.

Although ALE processes can smooth sidewall or line edge roughness, itcannot change CD variation e.g. line width or hole/pillar diameters. Todo this, a selective carbon-containing material deposition process isused to selectively deposit on photoresist structures and preferentiallyfill features with carbon-containing materials at different depositionrates into features of different sizes. In various embodiments, thediameters of holes or pillars are uniform over the substrate and LCDU isimproved. For example, methane (CH₄) may be used in some embodiments.

Returning to FIG. 1, 182 a-182 c show an example schematic illustrationof selective deposition processes that may be performed in accordancewith certain disclosed embodiments. For the selective polymerdeposition, 182 a shows a substrate with carbon atoms. In 182 b, thecarbon is exposed to a carbon-containing chemistry such as methane (CH₄)such that carbon material selectively deposits onto the surface of thesubstrate. Although methane is shown as an example, othercarbon-containing chemistries can be used which may have a chemicalformula of C_(x)H_(y), where x and y are integers greater than or equalto 1. Selective carbon deposition may be performed with low bias (e.g.,self-bias power=about 5V to about 15V) and low RF plasma power in therange of about 30 W to about 500 W. In some embodiments, thecarbon-containing chemistry may be combined with one or more diluents togenerate a plasma. Example diluents include nitrogen, helium, argon,hydrogen, and combinations thereof. In 182 c, the chamber is purged toremove excess polymer. The polymer remains on the surface of the carbonsubstrate.

FIG. 4 shows how selective polymer deposition can reduce the presence ofcrevices and protrusions on a photoresist. During 182 b, thecarbon-containing chemistry, such as methane, is delivered to thesubstrate and adsorbs to the surface of the carbon-containing materialon the substrate. In various embodiments, where there are crevices, suchas the crevice 450 shown in the photoresist substrate 400 of FIG. 4,deposition of a carbon-containing material 401 using a self-limitingprocess as described herein fills in these crevices 450 withcarbon-containing material, thereby smoothening the surface. As shown inFIG. 4, selective deposition may also include deposition on protrusions(499), such as on a photoresist. Without being bound by a particulartheory, it is believed that since the scale of the crevices on thesurface of the carbon-containing material may be on the atomic level,depositing a carbon-containing material into these crevices such thatcarbon-containing material is adsorbed uniformly onto the surface of thesubstrate will result in more material being deposited in a crevice thanon the adjacent relatively flat surface of the substrate, therebyreducing the presence of crevices with each deposition cycle.

In some embodiments, the substrate may also be exposed to an inertplasma after exposing the substrate to the carbon-containing chemistry.The inert plasma may be generated by flowing any one or more ofhydrogen, helium, nitrogen, argon, and neon and igniting a plasma. Theplasma may be ignited using a plasma power between about 30 W and about500 W. Without being bound by a particular theory, it is believed thatexposing the substrate to the inert plasma allows the adjacent surfaceto the carbon-containing material on the substrate such as a photoresistto be slightly etched and/or refreshed to prevent deposition, henceresulting in selective deposition. Exposures to the carbon-containingchemistry and inert plasma may be performed in one or more cycles.

Using a combination of ALE techniques as described herein and selectivedeposition, carbon-containing materials on a substrate may be processedto result in smoothened, uniform features, particularly for EUVapplications.

FIG. 5 is a process flow diagram of an embodiment whereby ALE andselective carbon deposition are performed. Operations of FIG. 5 may beperformed in a chamber having a chamber pressure between about 5 mTorrand about 100 mTorr. Operations of FIG. 5 may be performed at asubstrate temperature between about 0° C. and about 120° C. or betweenabout 20° C. and about 60° C. Substrate temperature will be understoodto mean the temperature at which the pedestal or wafer holder whichholds the substrate is set at. The operations shown in FIG. 5 summarizeoperations performed as described above with respect to FIG. 1. Forexample, in operation 402, a substrate including a carbon-containingmaterial is provided to a chamber. As described above, thecarbon-containing material may include a photoresist, or graphene, oramorphous carbon. Operation 402 may correspond with the schematicillustration depicted in 171 a and 172 a of FIG. 1. In operation 403,the substrate is exposed to a modification chemistry such as a strong ora weak oxidant to modify a surface of the substrate. In variousdisclosed embodiments, the carbon-containing material on the surface ismodified. This operation may correspond with the schematic illustrationdepicted in 171 b and 172 b of FIG. 1 and FIG. 2. In operation 405, thechamber is optionally purged to remove excess modification chemistry(such as a weak oxidant, i.e. CO₂) from the chamber. This operation maycorrespond to 172 d of FIGS. 1 and 3. The chamber may be purged byevacuating the chamber or stopping the flow of the modificationchemistry and flowing a non-reactive inert gas, such as helium or argon,to remove the excess gas phase modification chemistry. In operation 407,the substrate is exposed to an inert gas plasma to remove the modifiedsurface. During operation 407 a bias is applied to generate enoughenergy for the inert gas plasma to remove the modified surface withoutsputtering the substrate. In operation 409, the chamber is optionallypurged to remove modified material in gas phase from the chamber. Inoperation 411, the operations 403-409 may be optionally repeated incycles. In operation 423, the substrate is exposed to acarbon-containing chemistry to adsorb a layer of carbon-containingmaterial onto the substrate. This may be used in some embodiments tofill crevices on the carbon-containing surface of the substrate. Thisoperation may correspond to 182 a of FIGS. 1 and 4. In operation 424,the substrate is optionally exposed to an inert gas plasma to passivateregions of the substrate and allow selective deposition in subsequentcycles. In some embodiments, the chamber may be purged betweenperforming operations 423 and 424. In some embodiments, the substratemay be purged one or more times between performing any of the describedoperations. In various embodiments, operations 423 and 424 may beoptionally repeated in cycles and cycles may be performed with orwithout purge operations between performing operations 423 and 424. Inoperation 425, the chamber may be optionally purged. It will beunderstood that purging operations as described herein may be performedby pumping gases from the chamber, by flowing one or more inert gases,or combinations thereof using any suitable purging technique. Inoperation 498, it is determined whether the substrate has beensufficiently etched to form the desired surface on the substrate. Ifnot, operations 403-498 may be optionally repeated for n cycles, where nis an integer equal to or greater than 1. In some embodiments,operations 423-425 are repeated only in some but not all repeatedcycles, while in some embodiments, operations 423-425 are repeated inevery cycle.

By combining ALE process and the selective deposition process, both LCDUand LER of photoresist features are improved. This improvement is thentransferred to an underlying hard mask (such as a SiO₂/SiN layer), andconsequently to structures of interest resulting in improved variabilityand performance of the devices.

The ALE operations are gentle and precise which removes a digital amountof material per cycle so can be easily controlled to not overetch thesoft resist material. Similarly, the carbon-based selective depositionuses very low source power (e.g., transformer couple plasma or TCP) andno bias, and deposition can be performed without damaging the resist.

In some embodiments, selective carbon deposition may be optional. Forexample, these certain embodiments may be used in applications wherecritical dimension increase can be tolerated.

In certain embodiments, a combination of disclosed ALE operations andselective carbon deposition may be used on a carbon-containing materialto improve LCDU and recover the critical dimension if the originalcritical dimension is to be maintained throughout a patterning processusing a photoresist.

Apparatus

Disclosed embodiments may be performed in any suitable etching chamberor apparatus, such as the Kiyo® FX, available from Lam ResearchCorporation of Fremont, Calif. Another example of a plasma etch chamberthat may be employed is a Flex™ reactive ion etch tool available fromLam Research Corp. of Fremont, Calif. Further description of plasma etchchambers may be found in U.S. Pat. Nos. 6,841,943 and 8,552,334, whichare herein incorporated by reference in their entireties.

In some embodiments, an inductively coupled plasma (ICP) reactor may beused. One example is provided in FIG. 6. Such ICP reactors have alsobeen described in U.S. Pat. No. 9,362,133 issued Jun. 7, 2016, filedDec. 10, 2013, and titled “METHOD FOR FORMING A MASK BY ETCHINGCONFORMAL FILM ON PATTERNED ASHABLE HARDMASK,” hereby incorporated byreference for the purpose of describing a suitable ICP reactor forimplementation of the techniques described herein. Although ICP reactorsare described herein, in some embodiments, it should be understood thatcapacitively coupled plasma reactors may also be used. An exampleetching chamber or apparatus may include a chamber having chamber walls,a chuck for holding a substrate or wafer to be processed which mayinclude electrostatic electrodes for chucking and dechucking a wafer andmay be electrically charged using an RF power supply, an RF power supplyconfigured to supply power to a coil to generate a plasma, and gas flowinlets for inletting gases as described herein. For example,modification chemistry gases and/or selective deposition chemistry maybe flowed to the etching chamber for performing ALE and/or selectivedeposition respectively. In some embodiments, an apparatus may includemore than one chamber, each of which may be used to etch, deposit, orprocess substrates. The chamber or apparatus may include a systemcontroller for controlling some or all of the operations of the chamberor apparatus such as modulating the chamber pressure, inert gas flow,plasma power, plasma frequency, reactive gas flow (e.g., weak oxidantgas, carbon-containing gas, etc.); bias power, temperature, vacuumsettings; and other process conditions. The chamber may also be used toselectively deposit carbon-containing material onto a substrate.

FIG. 6 schematically shows a cross-sectional view of an inductivelycoupled plasma integrated etching and deposition apparatus 600appropriate for implementing certain embodiments herein, an example ofwhich is a Kiyo™ reactor, produced by Lam Research Corp. of Fremont,Calif. The inductively coupled plasma apparatus 600 includes an overallprocess chamber 601 structurally defined by chamber walls and a window611. The chamber walls may be fabricated from stainless steel oraluminum. The window 611 may be fabricated from quartz or otherdielectric material. An optional internal plasma grid 650 divides theoverall processing chamber 601 into an upper sub-chamber 602 and a lowersub-chamber 603. In most embodiments, plasma grid 650 may be removed,thereby utilizing a chamber space made of sub-chambers 602 and 603. Achuck 617 is positioned within the lower sub-chamber 603 near the bottominner surface. The chuck 617 is configured to receive and hold asemiconductor wafer 619 upon which the etching and deposition processesare performed. The chuck 617 can be an electrostatic chuck forsupporting the wafer 619 when present. In some embodiments, an edge ring(not shown) surrounds chuck 617, and has an upper surface that isapproximately planar with a top surface of a wafer 619, when presentover chuck 617. The chuck 617 also includes electrostatic electrodes forchucking and dechucking the wafer. A filter and DC clamp power supply(not shown) may be provided for this purpose. Other control systems forlifting the wafer 619 off the chuck 617 can also be provided. The chuck617 can be electrically charged using an RF power supply 623. The RFpower supply 623 is connected to matching circuitry 621 through aconnection 627. The matching circuitry 621 is connected to the chuck 617through a connection 625. In this manner, the RF power supply 623 isconnected to the chuck 617.

Elements for plasma generation include a coil 633 is positioned abovewindow 611. In some embodiments, a coil is not used in disclosedembodiments. The coil 633 is fabricated from an electrically conductivematerial and includes at least one complete turn. The example of a coil633 shown in FIG. 6 includes three turns. The cross-sections of coil 633are shown with symbols, and coils having an “X” extend rotationally intothe page, while coils having a “●” extend rotationally out of the page.Elements for plasma generation also include an RF power supply 641configured to supply RF power to the coil 633. In general, the RF powersupply 641 is connected to matching circuitry 639 through a connection645. The matching circuitry 639 is connected to the coil 633 through aconnection 643. In this manner, the RF power supply 641 is connected tothe coil 633. An optional Faraday shield 649 is positioned between thecoil 633 and the window 611. The Faraday shield 649 is maintained in aspaced apart relationship relative to the coil 633. The Faraday shield649 is disposed immediately above the window 611. The coil 633, theFaraday shield 649, and the window 611 are each configured to besubstantially parallel to one another. The Faraday shield may preventmetal or other species from depositing on the dielectric window of theplasma chamber 601.

Process gases (e.g. oxygen, carbon dioxide, methane, etc.) may be flowedinto the processing chamber 601 through one or more main gas flow inlets660 positioned in the upper sub-chamber 602 and/or through one or moreside gas flow inlets 670. Likewise, though not explicitly shown, similargas flow inlets may be used to supply process gases to a capacitivelycoupled plasma processing chamber. A vacuum pump, e.g., a one or twostage mechanical dry pump and/or turbomolecular pump 640, may be used todraw process gases out of the process chamber 601 and to maintain apressure within the process chamber 601. For example, the pump may beused to evacuate the chamber 601 during a purge operation of ALD. Avalve-controlled conduit may be used to fluidically connect the vacuumpump to the processing chamber 601 so as to selectively controlapplication of the vacuum environment provided by the vacuum pump. Thismay be done employing a closed-loop-controlled flow restriction device,such as a throttle valve (not shown) or a pendulum valve (not shown),during operational plasma processing. Likewise, a vacuum pump and valvecontrolled fluidic connection to the capacitively coupled plasmaprocessing chamber may also be employed.

During operation of the apparatus, one or more process gases may besupplied through the gas flow inlets 660 and/or 670. In certainembodiments, process gas may be supplied only through the main gas flowinlet 660, or only through the side gas flow inlet 670. In some cases,the gas flow inlets shown in the figure may be replaced more complex gasflow inlets, one or more showerheads, for example. The Faraday shield649 and/or optional grid 650 may include internal channels and holesthat allow delivery of process gases to the chamber 601. Either or bothof Faraday shield 649 and optional grid 650 may serve as a showerheadfor delivery of process gases. In some embodiments, a liquidvaporization and delivery system may be situated upstream of the chamber601, such that once a liquid reactant or precursor is vaporized, thevaporized reactant or precursor is introduced into the chamber 601 via agas flow inlet 660 and/or 670.

Radio frequency power is supplied from the RF power supply 641 to thecoil 633 to cause an RF current to flow through the coil 633. The RFcurrent flowing through the coil 633 generates an electromagnetic fieldabout the coil 633. The electromagnetic field generates an inductivecurrent within the upper sub-chamber 602. The physical and chemicalinteractions of various generated ions and radicals with the wafer 619selectively etch features of and deposit layers on the wafer.

If the plasma grid is used such that there is both an upper sub-chamber602 and a lower sub-chamber 603, the inductive current acts on the gaspresent in the upper sub-chamber 602 to generate an electron-ion plasmain the upper sub-chamber 602. The optional internal plasma grid 650limits the amount of hot electrons in the lower sub-chamber 603. In someembodiments, the apparatus is designed and operated such that the plasmapresent in the lower sub-chamber 603 is an ion-ion plasma.

Both the upper electron-ion plasma and the lower ion-ion plasma maycontain positive and negative ions, though the ion-ion plasma will havea greater ratio of negative ions to positive ions. Volatile etchingand/or deposition byproducts may be removed from the lower-sub-chamber603 through port 622. The chuck 617 disclosed herein may operate atelevated temperatures ranging between about 10° C. and about 250° C. Thetemperature will depend on the process operation and specific recipe.

Chamber 601 may be coupled to facilities (not shown) when installed in aclean room or a fabrication facility. Facilities include plumbing thatprovide processing gases, vacuum, temperature control, and environmentalparticle control. These facilities are coupled to chamber 601, wheninstalled in the target fabrication facility. Additionally, chamber 601may be coupled to a transfer chamber that allows robotics to transfersemiconductor wafers into and out of chamber 601 using typicalautomation.

In some embodiments, a system controller 630 (which may include one ormore physical or logical controllers) controls some or all of theoperations of a processing chamber. The system controller 630 mayinclude one or more memory devices and one or more processors. In someembodiments, the apparatus includes a switching system for controllingflow rates and durations when disclosed embodiments are performed. Insome embodiments, the apparatus may have a switching time of up to about500 ms, or up to about 750 ms. Switching time may depend on the flowchemistry, recipe chosen, reactor architecture, and other factors.

The processing chamber 601 or apparatus may include a system controller.For example, in some embodiments, a controller 630 is part of a system,which may be part of the above-described examples. Such systems caninclude semiconductor processing equipment, including a processing toolor tools, chamber or chambers, a platform or platforms for processing,and/or specific processing components (a wafer pedestal, a gas flowsystem, etc.). These systems may be integrated with electronics forcontrolling their operation before, during, and after processing of asemiconductor wafer or substrate. The electronics may be referred to asthe “controller,” which may control various components or subparts ofthe system or systems. The controller 630, depending on the processingrequirements and/or the type of system, may be programmed to control anyof the processes disclosed herein, including the delivery of processinggases, temperature settings (e.g., heating and/or cooling), pressuresettings, vacuum settings, power settings, radio frequency (RF)generator settings, RF matching circuit settings, frequency settings,flow rate settings, fluid delivery settings, positional and operationsettings, wafer transfers into and out of a tool and other transfertools and/or load locks connected to or interfaced with a specificsystem.

Broadly speaking, the controller 630 may be defined as electronicshaving various integrated circuits, logic, memory, and/or software thatreceive instructions, issue instructions, control operation, enablecleaning operations, enable endpoint measurements, and the like. Theintegrated circuits may include chips in the form of firmware that storeprogram instructions, digital signal processors (DSPs), chips defined asapplication specific integrated circuits (ASICs), and/or one or moremicroprocessors, or microcontrollers that execute program instructions(e.g., software). Program instructions may be instructions communicatedto the controller in the form of various individual settings (or programfiles), defining operational parameters for carrying out a particularprocess on or for a semiconductor wafer or to a system. The operationalparameters may, in some embodiments, be part of a recipe defined byprocess engineers to accomplish one or more processing steps during thefabrication of one or more layers, materials, metals, oxides, silicon,silicon dioxide, surfaces, circuits, and/or dies of a wafer.

The controller 630, in some implementations, may be a part of or coupledto a computer that is integrated with, coupled to the system, otherwisenetworked to the system, or a combination thereof. For example, thecontroller 630 may be in the “cloud” or all or a part of a fab hostcomputer system, which can allow for remote access of the waferprocessing. The computer may enable remote access to the system tomonitor current progress of fabrication operations, examine a history ofpast fabrication operations, examine trends or performance metrics froma plurality of fabrication operations, to change parameters of currentprocessing, to set processing steps to follow a current processing, orto start a new process. In some examples, a remote computer (e.g. aserver) can provide process recipes to a system over a network, whichmay include a local network or the Internet. The remote computer mayinclude a user interface that enables entry or programming of parametersand/or settings, which are then communicated to the system from theremote computer. In some examples, the controller receives instructionsin the form of data, which specify parameters for each of the processingsteps to be performed during one or more operations. It should beunderstood that the parameters may be specific to the type of process tobe performed and the type of tool that the controller is configured tointerface with or control. Thus as described above, the controller maybe distributed, such as by including one or more discrete controllersthat are networked together and working towards a common purpose, suchas the processes and controls described herein. An example of adistributed controller for such purposes would be one or more integratedcircuits on a chamber in communication with one or more integratedcircuits located remotely (such as at the platform level or as part of aremote computer) that combine to control a process on the chamber.

Without limitation, example systems may include a plasma etch chamber ormodule, a deposition chamber or module, a spin-rinse chamber or module,a metal plating chamber or module, a clean chamber or module, a beveledge etch chamber or module, a physical vapor deposition (PVD) chamberor module, a chemical vapor deposition (CVD) chamber or module, anatomic layer deposition (ALD) chamber or module, an atomic layer etch(ALE) chamber or module, an ion implantation chamber or module, a trackchamber or module, and any other semiconductor processing systems thatmay be associated or used in the fabrication and/or manufacturing ofsemiconductor wafers.

As noted above, depending on the process step or steps to be performedby the tool, the controller 630 might communicate with one or more ofother tool circuits or modules, other tool components, cluster tools,other tool interfaces, adjacent tools, neighboring tools, tools locatedthroughout a factory, a main computer, another controller, or tools usedin material transport that bring containers of wafers to and from toollocations and/or load ports in a semiconductor manufacturing factory.

The processing chamber 601 may be integrated in a multi-station toolsuch as shown in FIG. 7. Each station may be used to process differentoperations. For example, one station may be used to perform ALE whileanother station is used to perform selective deposition. Disclosedembodiments may be performed without breaking vacuum and may beperformed in the same apparatus. In various embodiments, ALE andselective deposition are performed without breaking vacuum. In variousembodiments, ALE and selective deposition are performed in the samechamber.

FIG. 7 depicts a semiconductor process cluster architecture with variousmodules that interface with a vacuum transfer module 738 (VTM). Thearrangement of transfer modules to “transfer” wafers among multiplestorage facilities and processing modules may be referred to as a“cluster tool architecture” system. Airlock module 730, also known as aloadlock or transfer module, is shown in VTM 738 with four processingmodules 720 a-720 d, which may be individual optimized to performvarious fabrication processes. By way of example, processing modules 720a-720 d may be implemented to perform substrate etching, deposition, ionimplantation, wafer cleaning, sputtering, and/or other semiconductorprocesses. In some embodiments, ALE and selective deposition areperformed in the same module. In some embodiments, ALE and selectivedeposition are performed in different modules of the same tool. One ormore of the substrate etching processing modules (any of 720 a-720 d)may be implemented as disclosed herein, i.e., for performing ALE,selectively depositing carbon-containing material, and other suitablefunctions in accordance with the disclosed embodiments. Airlock module730 and process module 720 may be referred to as “stations.” Eachstation has a facet 736 that interfaces the station to VTM 738. Insideeach facet, sensors 1-18 are used to detect the passing of wafer 726when moved between respective stations.

Robot 722 transfers wafer 726 between stations. In one embodiment, robot722 has one arm, and in another embodiment, robot 722 has two arms,where each arm has an end effector 724 to pick wafers such as wafer 726for transport. Front-end robot 732, in atmospheric transfer module (ATM)740, is used to transfer wafers 726 from cassette or Front OpeningUnified Pod (FOUP) 734 in Load Port Module (LPM) 742 to airlock module730. Module center 728 inside process module 720 is one location forplacing wafer 726. Aligner 744 in ATM 740 is used to align wafers.

In an exemplary processing method, a wafer is placed in one of the FOUPs734 in the LPM 742. Front-end robot 732 transfers the wafer from theFOUP 734 to an aligner 744, which allows the wafer 726 to be properlycentered before it is etched or processed. After being aligned, thewafer 726 is moved by the front-end robot 732 into an airlock module730. Because airlock modules have the ability to match the environmentbetween an ATM and a VTM, the wafer 726 is able to move between the twopressure environments without being damaged. From the airlock module730, the wafer 726 is moved by robot 722 through VTM 738 and into one ofthe process modules 720 a-720 d. In order to achieve this wafermovement, the robot 722 uses end effectors 724 on each of its arms. Oncethe wafer 726 has been processed, it is moved by robot 722 from theprocess modules 720 a-720 d to an airlock module 730. From here, thewafer 726 may be moved by the front-end robot 732 to one of the FOUPs734 or to the aligner 744.

It should be noted that the computer controlling the wafer movement canbe local to the cluster architecture, or can be located external to thecluster architecture in the manufacturing floor, or in a remote locationand connected to the cluster architecture via a network. A controller asdescribed above with respect to FIG. 6 may be implemented with the toolin FIG. 7.

EXPERIMENTAL Experiment 1

An experiment was conducted on a carbon-containing photoresist. Thesubstrate prior to etching processes is shown in FIG. 8A.

Conventional RIE etching is performed by exposing the substrate to HBrand a plasma power of 900 W for 15 seconds at 20° C. The resultingsubstrate is in FIG. 8B.

In another trial, the substrate was exposed to 10 cycles of ALE at 60°C. The operations included exposure to CO₂ plasma, purge, exposure tohelium plasma with a low bias, and purge. The resulting photoresist hassmooth sidewalls and reduced roughness, with improvement of LER.Stringers were reduced and scum of the photoresist was reduced. Theresulting substrate is in FIG. 8C.

In another trial, the substrate was exposed to 10 cycles of ALE at 20°C. The operations included exposure to CO₂ plasma, purge, exposure tohelium plasma with a low bias, and purge. The resulting substrate isshown in FIG. 8D.

In another trial, the substrate was exposed to 10 cycles of ALE at 60°C. The operations included exposure to CO₂ plasma, purge, exposure tohelium plasma with a low bias, and purge. The resulting substrate isshown in FIG. 8E.

Performing ALE resulted in a substrate having visibly smoother lines.These results suggest that ALE may be performed at either 20° C.

Experiment 2

An experiment was conducted whereby ALE of a photoresist was performedfor 3 cycles, and for 5 cycles. The substrate with no ALE is shown inFIGS. 9A-9C.

A substrate was exposed to three cycles of ALE operations which includedexposure to CO₂ plasma, purge, exposure to helium plasma with a lowbias, and purge. The substrate after 3 cycles is shown in FIGS. 10A-10C.

A substrate was exposed to five cycles of ALE operations which includedexposure to CO₂ plasma, purge, exposure to helium plasma with a lowbias, and purge. The substrate after 5 cycles is shown in FIGS. 11A-11C.

CONCLUSION

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications may be practiced within the scope ofthe disclosed embodiments. It should be noted that there are manyalternative ways of implementing the processes, systems, and apparatusof the present embodiments. Accordingly, the present embodiments are tobe considered as illustrative and not restrictive, and the embodimentsare not to be limited to the details given herein.

What is claimed is:
 1. A method of processing substrates, the methodcomprising: (a) exposing a substrate comprising a first carboncontaining material to an oxidant and igniting a first plasma with afirst bias power to modify a surface of the first carbon containingmaterial; and (b) exposing the modified surface to a second plasma at asecond bias power and for a duration sufficient to remove the modifiedsurface without sputtering.
 2. The method of claim 1, further comprising(c) selectively depositing a second carbon containing material on thesubstrate to fill crevices on the first carbon containing material. 3.The method of claim 1, wherein the second bias power may be betweenabout 30V and about 100V.
 4. The method of claim 1, wherein the oxidantis a strong oxidant.
 5. The method of claim 4, wherein the strongoxidant is oxygen.
 6. The method of claim 4, wherein the first plasma isgenerated using a plasma power between about 15 W and about 500 W. 7.The method of claim 4, wherein the first bias power is between about 5Vand 50V.
 8. The method of claim 1, wherein the oxidant is a weakoxidant.
 9. The method of claim 8, wherein the weak oxidant is selectedfrom the group consisting of carbon dioxide, carbon monoxide, sulfurdioxide, nitric oxide, nitrogen, and ammonia.
 10. The method of claim 8,wherein the first plasma is generated using a plasma power between about30 W and about 500 W.
 11. The method of claim 8, wherein the first biaspower is between about 30V and about 100V.
 12. The method of claim 2,wherein selectively depositing the second carbon containing material onthe substrate comprises applying a self bias at a power between about 5Vand about 15V and igniting a plasma using a plasma power between about30 W and about 500 W.
 13. The method of claim 12, wherein selectivelydepositing the second carbon containing material on the substratefurther comprises introducing methane.
 14. The method of claim 13,wherein selectively depositing the second carbon containing material onthe substrate further comprises introducing a diluent selected from thegroup consisting of nitrogen, helium, argon, hydrogen, and combinationsthereof.
 15. The method of claim 1, wherein the first carbon containingmaterial is selected from the group consisting of photoresist, amorphouscarbon, and graphene.
 16. The method of claim 1, wherein the firstcarbon containing material is a photoresist patterned by extremeultraviolet lithography.
 17. The method of claim 2, wherein (c)comprises exposing the substrate to methane to adsorb a layer of methaneto the surface of the first carbon containing material and exposing thesubstrate to a third plasma.
 18. The method of claim 17, wherein thethird plasma is generated by introducing an inert gas selected from thegroup consisting of helium, hydrogen, nitrogen, argon, and neon andigniting the third plasma.
 19. The method of claim 1, wherein exposingthe substrate comprising the first carbon containing material to theoxidant further comprises exposing the substrate to a diluent inert gasselected from the group consisting of helium, argon, neon, krypton, andxenon.
 20. The method of claim 1, wherein the second plasma in (b) isgenerated by introducing an inert gas selected from the group consistingof hydrogen, helium, nitrogen, argon, and neon and igniting the secondplasma.
 21. The method of claim 1, further comprising purging a chamberhousing the substrate between performing (a) and (b) to remove excessoxidant from the chamber.
 22. The method of claim 1, further comprisingrepeating (a) and (b) in cycles.
 23. The method of claim 2, furthercomprising repeating (a) (c) in cycles.
 24. The method of claim 1,wherein the substrate is housed on a pedestal set to a temperaturebetween about 0° C. and about 120° C.